I'm starting to put together my AR-15 and I'm worried that some parts will not fit together. I guess this whole issue stems from the fact that I bought an off-brand lower, (Roggio Arsenal, www.roggioarsenalusa.com), and was wondering if I should buy an upper to match the lower (ie: same brand) or if wont make too big a difference. But if I do buy the same brand, where do I stop? Will I have compatibility issues if I get a BCG from a different manufacturer? Will there be compatibility issues if I get a barrel from a different manufacturer? I think you get my point. (I should have bought the RRA lower.... (beats head against wall))

Also, if I don't buy an assembled upper, and have to run my own gas line and stuff, how difficult is that? Should that be taken to a gunny? Or is it easier than it sounds.

I've also been worried about head space. I'm not entirely sure what that is yet, but from what I gather, its a quality that the barrel has that is not affected by the upper? So if I buy my parts for the upper one by one, would i run into head space issues?

I've already bought a lower parts kit, from DPMS and a stock also from DPMS, but other than that, I'm still deciding on parts.

Thanks for your time and I appreciate any help or input that you've got on this issue.

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As long as everything is in spec you should not have issues mixing and matching brands. As far as buying the upper reciever and barrel seperatley and installing the gas tube goes, none of it is exceptionally hard but you do want to make sure you have the right tools and a vise block before you attempt it. The last thing you want to do is damage the components of the rifle.

As far has head spacing goes, again as long as everything is in spec and starting out with a new bolt operating in a new chamber everything should be good to go.

There are a zillion videos around.... brownells, midwayusa and youtube on how to do this stuff. there are a number of books as well. I thought highly of Walt's book and he helped me out when I got started with ARs.

Let me try to organize your questions:
1) Should you match the upper brand to the lower?

Not necessarily. If the upper and lower are both in spec, you'll have no problems (my go-to AR is a frankenrifle). If they aren't in spec, you're better off getting ones that are and ditching the crap.

2) Will you have barrel or BCG compatibility issues if you mix brands?

Nope. Again, in spec is in spec. Just buy a good BCG (like Bravo Company). Whatever you get, make sure the gas keys are staked properly.

3) How hard to assemble your own upper?

It isn't hard, but it takes special tools- an upper vise block (I like the DPMS Panther Claw), a barrel wrench, and a torque wrench. Honestly, for a first timer I'd just get a complete upper (like a Bravo Company- they may be a bit more, but may as well buy awesome the first time).

4) Headspacing

That is done when the barrel maker installs the barrel extension onto the barrel. While you could have tolerance stacking issues between the bolt and barrel, in practice I've not heard of it happening and the only remedy is to replace the bolt or barrel- you can't adjust the headspace because it would mean dinking with the orientation of the barrel extension relative to the gas port. Again, buy quality and it won't be a worry at all. Unless you think you're going to get into building ARs for kicks, you'll spend more on the tools to assemble the upper than you'll save by buying separate pieces. Better to just get a complete upper (with or without BCG).

4) Parts

So far it sounds like you're doing OK. Keep an eye on that parts kit the first time you use it- while I have built two with DPMS parts kits, the trigger and hammer pins both were walking on me no matter what I did, and I installed KNS pins to avoid that in the future- it would have been cheaper for me to buy a better parts kit to begin with.

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